Active shunt source-measure unit (smu) circuit

ABSTRACT

An active shunt source-measure unit (SMU) circuit can include an SMU or power supply having an active shunt circuit that is integrated with the current measuring sub-circuit of the SMU circuit. The active shunt circuit may be active during voltage sourcing of the SMU circuit and deactivated during current sourcing of the SMU circuit.

TECHNICAL FIELD

The disclosed technology pertains generally to source-measure unit (SMU)circuits and, more particularly, to the incorporating of certain aspectsof active shunt circuit technology into an SMU circuit.

BACKGROUND

A typical active shunt circuit generally uses gain and capacitance toproduce a virtual-impedance that is the actual resistance reduced by thegain. FIG. 1 is a circuit diagram illustrating an example of aconventional active shunt circuit 100. In the example, the active shuntcircuit 100 uses gain G₁(s) and capacitance C₀ to produce a virtualimpedance Z_(IN) that is the actual resistance R₀ reduced by the gain(α).

FIG. 2 is a circuit diagram illustrating a first example of aconventional two-range auto-ranging source-measure unit (SMU) circuit200. The SMU circuit 200 includes a a voltage source V-DAC, a currentsource I-DAC, and a first amplifier 206 electrically coupled with adevice under test (DUT).

The SMU circuit 200 also includes a second amplifier 208 electricallycoupled between the DUT and either the current source I-DAC or a buffer210 dependent upon the present position of a first switch S₁. First andsecond gain stage amplifiers 212, 214 are electrically coupled betweenthe DUT and either the voltage source V-DAC or the buffer 210 dependentupon the present position of a second switch S₂. A first resistor Ro iselectrically coupled with the DUT and the buffer 210. A second resistorR₁ is electrically coupled between the first resistor R₀ and the secondresistor R₁.

In the example, the SMU circuit 200 sources voltage across the DUT whenthe two switches S₁ and S₂ are in the down positions as shown in thefigure. The SMU circuit 200 has a control loop with an interactionbetween the DUT and the current sensing resistor that may be determinedby the following:

β=Z _(DUT) /Z _(DUT) +R _(S)

where R_(S) is either the first resistor R₀ or the second resistor R₁depending on which range is active.

In situations where the impedance of the DUT (Z_(DUT)) is smaller thanthe active range resistance R_(S), β becomes significantly less than oneand the control loop undesirably slows down.

FIG. 3 is a circuit diagram illustrating a second example of aconventional two-range auto-ranging source-measure unit (SMU) circuit300. In the example, the SMU circuit 300 uses a single control loop andswitch S₁ to transition between a voltage source V-DAC (i.e., when theswitch S₁ is in the down position as shown in the figure) and a currentsource I-DAC (i.e., when the switch S₁ is in the up position).

In this second example, the resistors R₀ and R₁ are arranged inparallel. This is in contrast to the SMU circuit 200 of the firstexample, in which the resistors R₀ and R₁ are in series.

SUMMARY

Embodiments of the disclosed technology are generally directed to sourcemeasure unit (SMU) circuits and, more particularly, to the incorporatingof active shunt circuit technology features into an SMU circuit. Incertain embodiments, an active shunt SMU circuit includes an SMU orpower supply having an active shunt circuit that is integrated with thecurrent measuring sub-circuit of the SMU circuit. The active shuntcircuit may be active during voltage sourcing of the SMU circuit anddeactivated during current sourcing of the SMU circuit, while in acurrent limit, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating an example of a conventionalactive shunt circuit.

FIG. 2 is a circuit diagram illustrating a first example of aconventional two-range auto-ranging source-measure unit (SMU) circuit.

FIG. 3 is a circuit diagram illustrating a second example of aconventional two-range auto-ranging source-measure unit (SMU) circuit.

FIG. 4 is a circuit diagram illustrating a first example of a two-rangeauto-ranging source-measure unit (SMU) circuit having an active shuntintegrated with the current measuring sub-circuit of the SMU circuit inaccordance with certain embodiments of the disclosed technology.

FIG. 5 is a circuit diagram illustrating a second example of a two-rangeauto-ranging source-measure unit (SMU) circuit having an active shuntintegrated with the current measuring sub-circuit of the SMU circuit inaccordance with certain embodiments of the disclosed technology.

DETAILED DESCRIPTION

Embodiments of the disclosed technology are generally directed tosource-measure unit (SMU) circuits. In certain embodiments, an activeshunt SMU circuit includes an SMU or power supply having an active shuntcircuit that is integrated with the current measuring sub-circuit of theSMU circuit. The active shunt circuit may be active during voltagesourcing of the SMU circuit and deactivated during current sourcing ofthe SMU circuit, while in a current limit, or both.

Active shunt circuitry is a relatively new technology that may be usedto improve the voltage sourcing performance of an SMU circuit. Because,however, an active shunt circuit may degrade the performance of the SMUcircuit when the SMU circuit switches from voltage sourcing to currentsourcing, embodiments may include deactivating the active shunt circuitwhen the SMU circuit is sourcing current. In such embodiments, thebenefits may still be achieved by the SMU circuit during voltagesourcing of the SMU circuit without the degradation performance thatwould otherwise occur during current sourcing of the SMU circuit.

The integration of an active shunt circuit into an SMU circuitadvantageously enables the SMU circuit to settle faster when sourcingvoltage. Such integration also enables the SMU circuit to remain stablewhile sourcing voltage into a larger capacitive load.

FIG. 4 is a circuit diagram illustrating a first example of a two-rangeauto-ranging source-measure unit (SMU) circuit 400 having an activeshunt integrated with the current measuring sub-circuit of the SMUcircuit 400 in accordance with certain embodiments of the disclosedtechnology. In the example, the SMU circuit 400 is substantiallyidentical to the SMU circuit 200 illustrated by FIG. 2 and, as such, thesame reference identifiers used in connection with the description ofFIG. 2 are also used in connection with the description of FIG. 4.Unlike the SMU circuit 200 illustrated by FIG. 2, however, an activeshunt circuit has been integrated into the SMU circuit 400 of FIG. 4 byway of two resistors R_(A) and R_(B) and two capacitors C₀ and C₁ andchanging the reference of the differential amplifier 206 from signal Sto ground.

The resistors R_(A) and R_(B) are added as feedback to the first andsecond gain stage amplifiers 212, 214 (G₀ and G₁), which limits the gainto α. The capacitors C₀ and C₁ are added across the first and secondresistors R₀ and R₁ such that their combined impedance rolls off at thesame frequency at which the gain of α rolls off.

Whereas the interaction between the device under test (DUT) and thecurrent sensing resistor in the SMU circuit 200 illustrated by FIG. 2may be determined by

${\beta = \frac{Z_{DUT}}{Z_{DUT} + H_{S}}},$

integration of the active shunt to R_(S) results in the following:

$\beta = \frac{Z_{DUT}}{Z_{DUT} + \frac{R_{S}}{\alpha}}$

where α represents the gain achieved by integration of the active shunt.

Consider an example in which α=100. In such example, the impedance ofthe DUT (Z_(DUT)) must be at least one hundred times smaller in orderfor β to be significantly less than one.

In the example illustrated by FIG. 4, the SMU circuit 400 sourcescurrent when both switches S₁ and S₂ are in the up position as shown inthe figure, i.e., by applying a known voltage across either R₀ or R₀+R₁.The added resistors (R_(A) and R_(B)) serve to limit the gain used tocontrol the voltage that is applied to these resistors. While theresulting applied voltage is not precisely the inversion of the I-DACvoltage, because the gain α is determined by the ratio of resistors itcan be precise and, thus, the I-DAC voltage can be predictably adjustedto correct the voltage in order to produce the desired current.

One having ordinary skill in the art will recognize that the samefeedback structure may be used for one-range SMU circuits or multi-rangeSMU circuits.

FIG. 5 is a circuit diagram illustrating a second example of a two-rangeauto-ranging source-measure unit (SMU) circuit 500 having an activeshunt integrated with the current measuring sub-circuit of the SMUcircuit 500 in accordance with certain embodiments of the disclosedtechnology. In the example, the SMU circuit 500 is substantiallyidentical to the SMU circuit 300 illustrated by FIG. 3 except for theaddition of an active shunt circuit by way of two resistors R_(A) andR_(B), two capacitors C₀ and C₁, a limited gain stage, and a secondswitch S₂. The second switch S₂ may be used to effectively remove ordeactivate the active shunt circuit during current sourcing by the SMUcircuit 500.

Having described and illustrated the principles of the invention withreference to illustrated embodiments, it will be recognized that theillustrated embodiments may be modified in arrangement and detailwithout departing from such principles, and may be combined in anydesired manner. And although the foregoing discussion has focused onparticular embodiments, other configurations are contemplated. Inparticular, even though expressions such as “according to an embodimentof the invention” or the like are used herein, these phrases are meantto generally reference embodiment possibilities, and are not intended tolimit the invention to particular embodiment configurations. As usedherein, these terms may reference the same or different embodiments thatare combinable into other embodiments.

Consequently, in view of the wide variety of permutations to theembodiments described herein, this detailed description and accompanyingmaterial is intended to be illustrative only, and should not be taken aslimiting the scope of the invention. What is claimed as the invention,therefore, is all such modifications as may come within the scope andspirit of the following claims and equivalents thereto.

We claim:
 1. A circuit for sourcing voltage and current to a deviceunder test (DUT), the circuit comprising: an output configured to beelectrically coupled with the DUT; and a power-providing circuitelectrically coupled with the output, wherein the power-providingcircuit is operable to regulate voltage applied to the output by varyingcurrent provided through the output, and wherein the power-providingcircuit is further operable to regulate the current provided through theoutput by varying the voltage applied to the output, the power-providingincluding at least one sense resistor in series with the output andoperable to measure the current provided through the output, wherein,when the power-providing circuit is regulating the voltage applied tothe output, a controlled feedback gain is applied to the at least onesense resistor to reduce apparent resistance to the voltage regulation.2. The circuit of claim 1, wherein, when the power-providing circuit isregulating the current provided through the output, the controlledfeedback gain is not applied to the at least one sense resistor.
 3. Thecircuit of claim 2, wherein the at least one sense resistor includes afirst resistor R₀ having a first end electrically coupled with theoutput.
 4. The circuit of claim 3, wherein the power-providing circuitincludes a first capacitor C₀ electrically coupled in parallel with thefirst resistor R₀.
 5. The circuit of claim 4, wherein thepower-providing circuit includes: a first amplifier electrically coupledwith the output; a second amplifier electrically coupled between theoutput and a first switch; a first gain stage amplifier electricallycoupled between the output and a second switch; a second gain stageamplifier electrically coupled between the output and the first gainstage amplifier; a second resistor R₁ electrically coupled between thethird amplifier and the first resistor R₀; and a second capacitor C₁electrically coupled in parallel with the second resistor R₁.
 6. Thecircuit of claim 5, further comprising two resistors R_(A) and R_(B)added as feedback to the first and second gain stage amplifiers.
 7. Thecircuit of claim 5, wherein the resistance of the second resistor R₁ isdefined by the following:R ₁=(k=1)R ₀
 8. The circuit of claim 5, wherein the capacitance of thesecond capacitor C₁ is defined by the following:C ₁ =C ₀/(k−1)
 9. The circuit of claim 5, wherein the first switch isconfigured to toggle a buffer that is electrically coupled with theoutput.
 10. The circuit of claim 9, wherein the second switch isconfigured to toggle the buffer, and further wherein no more than one ofthe first and second switches is electrically coupled with the buffer atany given time.
 11. The circuit of claim 9, wherein the second switch isconfigured to toggle a buffer that is electrically coupled with theoutput.